We discuss the theory, design, and performance of a flat-panel tactile display capable of controlling shear force on a finger. In previous research a TPaD variable friction device was presented. It modulates friction by using vertical ultrasonic vibrations to form a squeeze film of air between the finger and the horizontal glass surface. In this research, a TPaD is oscillated in the horizontal plane at 20-100Hz while alternating between low and high friction at the same frequency. As the plate moves in one direction, the squeeze film is turned on and friction is reduced. As the plate moves in the opposite direction, the squeeze film is turned off and the friction increases. The net time-averaged force is non-zero and can be used as a source of shear force to a finger in contact with the surface. We demonstrate the implementation of line sources and sinks using this new technology.